This invention relates to disposable cassettes for transporting sterile solutions, and more particularly to such cassettes for use in irrigation and aspiration systems for ophthalmic applications.
Much equipment used in surgical procedures now utilizes disposable units wherever this is economically feasible. Experiences with contamination of reused units and components, together with the availability of low cost but high performance moldable materials, have resulted in this trend. Consequently, where a sterile fluid or material is to be passed to a surgical site, or various sterile flows are to be combined, systems are designed so that each surgical procedure is carried out using a new tubing set. Further benefits are derived with these systems from the fact that peristaltic pumps, using movable rollers, can operate directly on the tubing exterior to advance the fluid, or conversely, to block flow in a tubing simply by externally pinching the tubing. Neither event affects the sterility of the internal tubing in ordinary operation.
In typical practice, presterilized disposable tubing sets are configured for particular applications, sometimes including small disposable accessories as well. Before use, the operator removes the tubing set from a sterile container or package and, under sterile conditions, makes the necessary attachments from point to point. It was evident, quite early in the usage of such sets, that some convenience and other advantages could be gained by incorporating the tubing in a cassette, arranged so as to eliminate the necessity for threading tubing through the operative parts of a machine. There are numerous examples of such disposable cassettes, including a number of tubing cassettes for use with peristaltic pumps. In exchange for the ease of installation, and the reduction in chance of operator error, disadvantages are presented in terms-of cost, the need in some instances for complex internal tubing paths that may involve sharp bends, and often the unsuitability of the cassette in the event of any modification, however minor, of the operative parts of the system.
A specific example of the problems involved is evidenced by U.S. Pat. No. 4,713,051 to Steppe et al. This unit is intended for usage with an irrigation/aspiration system for ophthalmic microsurgery. A sterile solution is fed via irrigation tubing through the top of a cassette housing, and around an element providing a backup surface or boss adjacent an opening in the leading edge of the cassette, which is inserted into the machine in edgewise fashion. A clamp is engageable against the tubing and the boss, to pinch the tubing and stop the passage of sterile solution out a side edge of the cassette toward a handpiece. Controls available to the surgeon enable aspiration of non-sterile fluid and tissue from the surgical site back through an aspiration line into a side edge of the cassette and out to an attached waste bag. A length of the tubing close to the front edge of the cassette is exposed adjacent a semicircular surface against which a peristaltic pump may be engaged so as to withdraw the aspiration fluid. A shunt line from the aspiration line, within the cassette, leads to a vacuum control system opening at the front edge, into which an occluder shaft fits so as to control the differential pressure level available in the aspiration manifold. By operating the controls, the surgeon or technician can open the shunt line to provide instant backflow of irrigation fluid so that cortical material that is caught in the handpiece can be immediately cleaned out.
The system shown in U.S. Pat. No. 4,713,051 has a number of practical disadvantages. The element or member which controls irrigation flow by pinching the irrigation line is a non-sterile member, and must be operated many times in the course of a surgical procedure. In the event of puncturing or fracturing the irrigation line, the result is exposure of the sterile irrigation fluid to contaminants. While leakage external to the cassette might be visible to the operator, leakage arising in the interior of the installed cassette cannot be observed, so that contamination would be carried to the surgical site. Another disadvantage is that the tubings, as mentioned, enter or exit from three different sides of the cassette, making the unit unwieldy to handle. In addition, the internal configuration involves sharp bends in the tubing which can give rise to kinking and substantial impedance to flow. The tubing sections can also shift and even come loose in this configuration and the length of the tubing involved necessitates priming with an excessive amount of sterile solution. Further, the attached bag is internally secured and cannot be changed except by replacing the entire cassette. In the event of a long surgical procedure, therefore, as the bag capacity is approached the only feasible expedient is cassette replacement.
As noted above, such a unit does not permit any degree of variation in the design of the system which is to receive it. Even changes of tubing sizes can result in outmoding of the particular cassette design. In point of fact, the design shown in the patent was outmoded by a change in the configuration of the system, known as the CooperVision 10,000, to incorporate a separate pinch valve based upon an earlier design, the CooperVision "KCP" machine. In the original 10,000 model, when a surgeon desired to terminate aspiration immediately, he placed the pedal control in position to operate the vacuum control system so as to break the suction. The modified system incorporated a feature of the KCP machine using a shunt between the incoming irrigation line and the vacuum control system (VCS) line, this shunt line being normally closed by a pinch valve. Opening the shunt pinch valve at the same time as aspiration suction is reduced provides a separate path for flow of irrigation solution into the aspiration line going to the handpiece. This positive backflow, referred to as "venting", is instantly provided to the operative site through the aspiration line to enable clearing the handpiece. This relatively modest change in the configuration of the system to employ a conventional feature necessitated a new cassette and substantially increased the difficulties mentioned as to the configuration of U.S. Pat. No. 4,713,051.
Another difficulty encountered with this system has not been resolved since the introduction of the shunt line. The internal tubing sections being relatively long, mechanical resonances appear as suction is applied during the delicate phase of aspirating while the surgeon is working within the capsule of the lens. The resonance in the system is transmitted during aspiration at the aspiration part of the handpiece and is not only disturbing to the surgeon but introduces unnecessary risk factors when working within the capsule.